Group by index + column in pandas

Question

I have a dataframe that has the columns

1. user_id
2. item_bought

Here user_id is the index of the df. I want to group by both user_id and item_b

Answer 1

import pandas as pd

import numpy as np

In [11]:

df = pd.DataFrame()

In [12]:

df['user_id'] = ['b','b','b','c']

In [13]:

df['item_bought'] = ['x','x','y','y']

In [14]:

df['ct'] = 1

In [15]:

df

Out[15]:
    user_id     item_bought     ct
0   b   x   1
1   b   x   1
2   b   y   1
3   c   y   1
In [16]:

pd.pivot_table(df,values='ct',index=['user_id','item_bought'],aggfunc=np.sum)

Out[16]:

user_id  item_bought
b        x              2
         y              1
c        y              1